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use crate::fx::FxHashMap;
use arrayvec::ArrayVec;
use itertools::Either;
use std::fmt;
use std::hash::Hash;
use std::ops::Index;
/// For pointer-sized arguments arrays
/// are faster than set/map for up to 64
/// arguments.
///
/// On the other hand such a big array
/// hurts cache performance, makes passing
/// sso structures around very expensive.
///
/// Biggest performance benefit is gained
/// for reasonably small arrays that stay
/// small in vast majority of cases.
///
/// '8' is chosen as a sane default, to be
/// reevaluated later.
const SSO_ARRAY_SIZE: usize = 8;
/// Small-storage-optimized implementation of a map.
///
/// Stores elements in a small array up to a certain length
/// and switches to `HashMap` when that length is exceeded.
//
// FIXME: Implements subset of HashMap API.
//
// Missing HashMap API:
// all hasher-related
// try_reserve
// shrink_to (unstable)
// drain_filter (unstable)
// into_keys/into_values (unstable)
// all raw_entry-related
// PartialEq/Eq (requires sorting the array)
// Entry::or_insert_with_key
// Vacant/Occupied entries and related
//
// FIXME: In HashMap most methods accepting key reference
// accept reference to generic `Q` where `K: Borrow<Q>`.
//
// However, using this approach in `HashMap::get` apparently
// breaks inlining and noticeably reduces performance.
//
// Performance *should* be the same given that borrow is
// a NOP in most cases, but in practice that's not the case.
//
// Further investigation is required.
//
// Affected methods:
// SsoHashMap::get
// SsoHashMap::get_mut
// SsoHashMap::get_entry
// SsoHashMap::get_key_value
// SsoHashMap::contains_key
// SsoHashMap::remove
// SsoHashMap::remove_entry
// Index::index
// SsoHashSet::take
// SsoHashSet::get
// SsoHashSet::remove
// SsoHashSet::contains
#[derive(Clone)]
pub enum SsoHashMap<K, V> {
Array(ArrayVec<(K, V), SSO_ARRAY_SIZE>),
Map(FxHashMap<K, V>),
}
impl<K, V> SsoHashMap<K, V> {
/// Creates an empty `SsoHashMap`.
#[inline]
pub fn new() -> Self {
SsoHashMap::Array(ArrayVec::new())
}
/// Creates an empty `SsoHashMap` with the specified capacity.
pub fn with_capacity(cap: usize) -> Self {
if cap <= SSO_ARRAY_SIZE {
Self::new()
} else {
SsoHashMap::Map(FxHashMap::with_capacity_and_hasher(cap, Default::default()))
}
}
/// Clears the map, removing all key-value pairs. Keeps the allocated memory
/// for reuse.
pub fn clear(&mut self) {
match self {
SsoHashMap::Array(array) => array.clear(),
SsoHashMap::Map(map) => map.clear(),
}
}
/// Returns the number of elements the map can hold without reallocating.
pub fn capacity(&self) -> usize {
match self {
SsoHashMap::Array(_) => SSO_ARRAY_SIZE,
SsoHashMap::Map(map) => map.capacity(),
}
}
/// Returns the number of elements in the map.
pub fn len(&self) -> usize {
match self {
SsoHashMap::Array(array) => array.len(),
SsoHashMap::Map(map) => map.len(),
}
}
/// Returns `true` if the map contains no elements.
pub fn is_empty(&self) -> bool {
match self {
SsoHashMap::Array(array) => array.is_empty(),
SsoHashMap::Map(map) => map.is_empty(),
}
}
/// An iterator visiting all key-value pairs in arbitrary order.
/// The iterator element type is `(&'a K, &'a V)`.
#[inline]
pub fn iter(&self) -> <&Self as IntoIterator>::IntoIter {
self.into_iter()
}
/// An iterator visiting all key-value pairs in arbitrary order,
/// with mutable references to the values.
/// The iterator element type is `(&'a K, &'a mut V)`.
#[inline]
pub fn iter_mut(&mut self) -> impl Iterator<Item = (&'_ K, &'_ mut V)> {
self.into_iter()
}
/// An iterator visiting all keys in arbitrary order.
/// The iterator element type is `&'a K`.
pub fn keys(&self) -> impl Iterator<Item = &'_ K> {
match self {
SsoHashMap::Array(array) => Either::Left(array.iter().map(|(k, _v)| k)),
SsoHashMap::Map(map) => Either::Right(map.keys()),
}
}
/// An iterator visiting all values in arbitrary order.
/// The iterator element type is `&'a V`.
pub fn values(&self) -> impl Iterator<Item = &'_ V> {
match self {
SsoHashMap::Array(array) => Either::Left(array.iter().map(|(_k, v)| v)),
SsoHashMap::Map(map) => Either::Right(map.values()),
}
}
/// An iterator visiting all values mutably in arbitrary order.
/// The iterator element type is `&'a mut V`.
pub fn values_mut(&mut self) -> impl Iterator<Item = &'_ mut V> {
match self {
SsoHashMap::Array(array) => Either::Left(array.iter_mut().map(|(_k, v)| v)),
SsoHashMap::Map(map) => Either::Right(map.values_mut()),
}
}
/// Clears the map, returning all key-value pairs as an iterator. Keeps the
/// allocated memory for reuse.
pub fn drain(&mut self) -> impl Iterator<Item = (K, V)> + '_ {
match self {
SsoHashMap::Array(array) => Either::Left(array.drain(..)),
SsoHashMap::Map(map) => Either::Right(map.drain()),
}
}
}
impl<K: Eq + Hash, V> SsoHashMap<K, V> {
/// Changes underlying storage from array to hashmap
/// if array is full.
fn migrate_if_full(&mut self) {
if let SsoHashMap::Array(array) = self {
if array.is_full() {
*self = SsoHashMap::Map(array.drain(..).collect());
}
}
}
/// Reserves capacity for at least `additional` more elements to be inserted
/// in the `SsoHashMap`. The collection may reserve more space to avoid
/// frequent reallocations.
pub fn reserve(&mut self, additional: usize) {
match self {
SsoHashMap::Array(array) => {
if SSO_ARRAY_SIZE < (array.len() + additional) {
let mut map: FxHashMap<K, V> = array.drain(..).collect();
map.reserve(additional);
*self = SsoHashMap::Map(map);
}
}
SsoHashMap::Map(map) => map.reserve(additional),
}
}
/// Shrinks the capacity of the map as much as possible. It will drop
/// down as much as possible while maintaining the internal rules
/// and possibly leaving some space in accordance with the resize policy.
pub fn shrink_to_fit(&mut self) {
if let SsoHashMap::Map(map) = self {
if map.len() <= SSO_ARRAY_SIZE {
*self = SsoHashMap::Array(map.drain().collect());
} else {
map.shrink_to_fit();
}
}
}
/// Retains only the elements specified by the predicate.
pub fn retain<F>(&mut self, mut f: F)
where
F: FnMut(&K, &mut V) -> bool,
{
match self {
SsoHashMap::Array(array) => array.retain(|(k, v)| f(k, v)),
SsoHashMap::Map(map) => map.retain(f),
}
}
/// Inserts a key-value pair into the map.
///
/// If the map did not have this key present, [`None`] is returned.
///
/// If the map did have this key present, the value is updated, and the old
/// value is returned. The key is not updated, though; this matters for
/// types that can be `==` without being identical. See the [module-level
/// documentation] for more.
pub fn insert(&mut self, key: K, value: V) -> Option<V> {
match self {
SsoHashMap::Array(array) => {
for (k, v) in array.iter_mut() {
if *k == key {
let old_value = std::mem::replace(v, value);
return Some(old_value);
}
}
if let Err(error) = array.try_push((key, value)) {
let mut map: FxHashMap<K, V> = array.drain(..).collect();
let (key, value) = error.element();
map.insert(key, value);
*self = SsoHashMap::Map(map);
}
None
}
SsoHashMap::Map(map) => map.insert(key, value),
}
}
/// Removes a key from the map, returning the value at the key if the key
/// was previously in the map.
pub fn remove(&mut self, key: &K) -> Option<V> {
match self {
SsoHashMap::Array(array) => {
array.iter().position(|(k, _v)| k == key).map(|index| array.swap_remove(index).1)
}
SsoHashMap::Map(map) => map.remove(key),
}
}
/// Removes a key from the map, returning the stored key and value if the
/// key was previously in the map.
pub fn remove_entry(&mut self, key: &K) -> Option<(K, V)> {
match self {
SsoHashMap::Array(array) => {
array.iter().position(|(k, _v)| k == key).map(|index| array.swap_remove(index))
}
SsoHashMap::Map(map) => map.remove_entry(key),
}
}
/// Returns a reference to the value corresponding to the key.
pub fn get(&self, key: &K) -> Option<&V> {
match self {
SsoHashMap::Array(array) => {
for (k, v) in array {
if k == key {
return Some(v);
}
}
None
}
SsoHashMap::Map(map) => map.get(key),
}
}
/// Returns a mutable reference to the value corresponding to the key.
pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
match self {
SsoHashMap::Array(array) => {
for (k, v) in array {
if k == key {
return Some(v);
}
}
None
}
SsoHashMap::Map(map) => map.get_mut(key),
}
}
/// Returns the key-value pair corresponding to the supplied key.
pub fn get_key_value(&self, key: &K) -> Option<(&K, &V)> {
match self {
SsoHashMap::Array(array) => {
for (k, v) in array {
if k == key {
return Some((k, v));
}
}
None
}
SsoHashMap::Map(map) => map.get_key_value(key),
}
}
/// Returns `true` if the map contains a value for the specified key.
pub fn contains_key(&self, key: &K) -> bool {
match self {
SsoHashMap::Array(array) => array.iter().any(|(k, _v)| k == key),
SsoHashMap::Map(map) => map.contains_key(key),
}
}
/// Gets the given key's corresponding entry in the map for in-place manipulation.
#[inline]
pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
Entry { ssomap: self, key }
}
}
impl<K, V> Default for SsoHashMap<K, V> {
#[inline]
fn default() -> Self {
Self::new()
}
}
impl<K: Eq + Hash, V> FromIterator<(K, V)> for SsoHashMap<K, V> {
fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> SsoHashMap<K, V> {
let mut map: SsoHashMap<K, V> = Default::default();
map.extend(iter);
map
}
}
impl<K: Eq + Hash, V> Extend<(K, V)> for SsoHashMap<K, V> {
fn extend<I>(&mut self, iter: I)
where
I: IntoIterator<Item = (K, V)>,
{
for (key, value) in iter.into_iter() {
self.insert(key, value);
}
}
#[inline]
fn extend_one(&mut self, (k, v): (K, V)) {
self.insert(k, v);
}
fn extend_reserve(&mut self, additional: usize) {
match self {
SsoHashMap::Array(array) => {
if SSO_ARRAY_SIZE < (array.len() + additional) {
let mut map: FxHashMap<K, V> = array.drain(..).collect();
map.extend_reserve(additional);
*self = SsoHashMap::Map(map);
}
}
SsoHashMap::Map(map) => map.extend_reserve(additional),
}
}
}
impl<'a, K, V> Extend<(&'a K, &'a V)> for SsoHashMap<K, V>
where
K: Eq + Hash + Copy,
V: Copy,
{
fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
self.extend(iter.into_iter().map(|(k, v)| (*k, *v)))
}
#[inline]
fn extend_one(&mut self, (&k, &v): (&'a K, &'a V)) {
self.insert(k, v);
}
#[inline]
fn extend_reserve(&mut self, additional: usize) {
Extend::<(K, V)>::extend_reserve(self, additional)
}
}
impl<K, V> IntoIterator for SsoHashMap<K, V> {
type IntoIter = Either<
<ArrayVec<(K, V), SSO_ARRAY_SIZE> as IntoIterator>::IntoIter,
<FxHashMap<K, V> as IntoIterator>::IntoIter,
>;
type Item = <Self::IntoIter as Iterator>::Item;
fn into_iter(self) -> Self::IntoIter {
match self {
SsoHashMap::Array(array) => Either::Left(array.into_iter()),
SsoHashMap::Map(map) => Either::Right(map.into_iter()),
}
}
}
/// adapts Item of array reference iterator to Item of hashmap reference iterator.
#[inline(always)]
fn adapt_array_ref_it<K, V>(pair: &(K, V)) -> (&K, &V) {
let (a, b) = pair;
(a, b)
}
/// adapts Item of array mut reference iterator to Item of hashmap mut reference iterator.
#[inline(always)]
fn adapt_array_mut_it<K, V>(pair: &mut (K, V)) -> (&K, &mut V) {
let (a, b) = pair;
(a, b)
}
impl<'a, K, V> IntoIterator for &'a SsoHashMap<K, V> {
type IntoIter = Either<
std::iter::Map<
<&'a ArrayVec<(K, V), SSO_ARRAY_SIZE> as IntoIterator>::IntoIter,
fn(&'a (K, V)) -> (&'a K, &'a V),
>,
<&'a FxHashMap<K, V> as IntoIterator>::IntoIter,
>;
type Item = <Self::IntoIter as Iterator>::Item;
fn into_iter(self) -> Self::IntoIter {
match self {
SsoHashMap::Array(array) => Either::Left(array.into_iter().map(adapt_array_ref_it)),
SsoHashMap::Map(map) => Either::Right(map.iter()),
}
}
}
impl<'a, K, V> IntoIterator for &'a mut SsoHashMap<K, V> {
type IntoIter = Either<
std::iter::Map<
<&'a mut ArrayVec<(K, V), SSO_ARRAY_SIZE> as IntoIterator>::IntoIter,
fn(&'a mut (K, V)) -> (&'a K, &'a mut V),
>,
<&'a mut FxHashMap<K, V> as IntoIterator>::IntoIter,
>;
type Item = <Self::IntoIter as Iterator>::Item;
fn into_iter(self) -> Self::IntoIter {
match self {
SsoHashMap::Array(array) => Either::Left(array.into_iter().map(adapt_array_mut_it)),
SsoHashMap::Map(map) => Either::Right(map.iter_mut()),
}
}
}
impl<K, V> fmt::Debug for SsoHashMap<K, V>
where
K: fmt::Debug,
V: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_map().entries(self.iter()).finish()
}
}
impl<'a, K, V> Index<&'a K> for SsoHashMap<K, V>
where
K: Eq + Hash,
{
type Output = V;
#[inline]
fn index(&self, key: &K) -> &V {
self.get(key).expect("no entry found for key")
}
}
/// A view into a single entry in a map.
pub struct Entry<'a, K, V> {
ssomap: &'a mut SsoHashMap<K, V>,
key: K,
}
impl<'a, K: Eq + Hash, V> Entry<'a, K, V> {
/// Provides in-place mutable access to an occupied entry before any
/// potential inserts into the map.
pub fn and_modify<F>(self, f: F) -> Self
where
F: FnOnce(&mut V),
{
if let Some(value) = self.ssomap.get_mut(&self.key) {
f(value);
}
self
}
/// Ensures a value is in the entry by inserting the default if empty, and returns
/// a mutable reference to the value in the entry.
#[inline]
pub fn or_insert(self, value: V) -> &'a mut V {
self.or_insert_with(|| value)
}
/// Ensures a value is in the entry by inserting the result of the default function if empty,
/// and returns a mutable reference to the value in the entry.
pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V {
self.ssomap.migrate_if_full();
match self.ssomap {
SsoHashMap::Array(array) => {
let key_ref = &self.key;
let found_index = array.iter().position(|(k, _v)| k == key_ref);
let index = if let Some(index) = found_index {
index
} else {
let index = array.len();
array.try_push((self.key, default())).unwrap();
index
};
&mut array[index].1
}
SsoHashMap::Map(map) => map.entry(self.key).or_insert_with(default),
}
}
/// Returns a reference to this entry's key.
#[inline]
pub fn key(&self) -> &K {
&self.key
}
}
impl<'a, K: Eq + Hash, V: Default> Entry<'a, K, V> {
/// Ensures a value is in the entry by inserting the default value if empty,
/// and returns a mutable reference to the value in the entry.
#[inline]
pub fn or_default(self) -> &'a mut V {
self.or_insert_with(Default::default)
}
}